& Allen, Mark B.
(2020). Diachronous Tibetan Plateau landscape evolution derived from lava field geomorphology. Geology 48
Author(s) from Durham
Evolution of the Tibetan Plateau is important for understanding continental tectonics because of the plateau’s exceptional elevation (~5 km above sea level) and crustal thickness (~70 km). Patterns of long-term landscape evolution can constrain tectonic processes, but have been hard to quantify, in contrast to established data sets for strain, exhumation, and paleo-elevation. This study analyzes the relief of the bases and tops of 17 Cenozoic lava fields on the central and northern Tibetan Plateau. Analyzed fields have typical lateral dimensions of tens of kilometers, and so have an appropriate scale for interpreting tectonic geomorphology. Fourteen of the fields have not been deformed since eruption. One field is cut by normal faults; two others are gently folded, with limb dips <6°. Relief of the bases and tops of the fields is comparable to that of modern, internally drained parts of the plateau, and distinctly lower than that of externally drained regions. The lavas preserve a record of underlying low-relief bedrock landscapes at the time they were erupted, which have undergone little change since. There is an overlap in each area between younger published low-temperature thermochronology ages and the age of the oldest eruption in each area, here interpreted as the transition between the end of significant (>3 km) exhumation and plateau landscape development. This diachronous process took place between ~32.5°N and ~36.5°N and between ca. 40 Ma and ca. 10 Ma, advancing northwards at a long-term rate of ~15 km/m.y. Results are consistent with incremental northward growth of the plateau, rather than a stepwise evolution or synchronous uplift.